Field of the Invention
One disclosed aspect of the embodiments relates to an imaging apparatus.
Description of the Related Art
In recent years, imaging apparatuses such as a digital still camera and a digital video camera have been widely spread in which captured images can be saved as digital data. Such an imaging apparatus includes image pickup devices such as a CMOS (Complementary Metal Oxide Semiconductor) type image sensor (hereinafter, CMOS sensor) which reads out pixel signals based on xy addressing scheme.
In a CMOS sensor, random access to pixels can be performed. Furthermore, compared with a CCD (Charge Coupled Device) type image sensor (hereinafter, CCD sensor), a signal can be read out at a higher speed from a CMOS sensor, which is highly sensitive and consumes less electric power.
Unlike a CCD sensor which directly transfers a signal charge having undergone photoelectric conversion in a pixel to an output circuit, a CMOS sensor outputs a pixel signal converted to voltage in each pixel by performing signal processing in a column circuit. Thus, noise occurring in the column circuit may be added to the pixel signal. Accordingly, as disclosed in Japanese Patent Laid-Open No. 2005-333462, a CMOS sensor may include a column amplifier in a column circuit, and a pixel signal is amplified in the column amplifier so that the ratio of noise in the column circuit to the pixel signal can be improved.
However, the amplification of a pixel signal in the column amplifier may increase the operating voltage of the column circuit, consuming an increased amount of electric power. In order to solve this problem, as disclosed in Japanese Patent Laid-Open No. 2005-323331, a CMOS sensor having an analog-digital (AD) converting circuit in a column circuit may not include a column amplifier for reduction of power consumption and operating voltage.
A CMOS sensor which does not have a column amplifier within a column circuit, as disclosed in Japanese Patent Laid-Open No. 2005-323331, may have column noise occurring in the column circuit. In order to reduce the column noise, a signal in one pixel may be read out a plurality of number of times, and the read signals are added every time.
However, because such signals are added after executing signal processing thereon in the column circuit in a CMOS sensor, the noise reduction processing may take time and thus significantly lower the frame rate, still disadvantageously.